The present invention is an apparatus and method for identifying unknown substances. This invention is particularly concerned with the recognition of large biological materials which are electrophoretically separated in a narrow bore capillary and which are then detected by measuring the amount of ultraviolet radiation absorbed by the unknown substances as they pass through a novel cell that resides within the capillary.
Recent advances in biotechnology have accelerated the demand of research laboratories, health-care facilities, and pharmaceutical manufacturers for devices which are capable of accurately and rapidly identifying extremely small quantities of inorganic and organic substances. Previous techniques, which include gas and liquid chromatography, have been employed to assay samples whose molecular structure is relatively small. Although chromatography may be successfully employed to resolve metals, inorganic mixtures, and small organic ions; the very large and exceedingly complex molecules of amino acids, proteins, peptides, and DNA are more difficult to isolate and discover in a sample of unknown composition. Another serious flaw in chromatographic methods is the predicament that is encountered when the unknown sample is especially sparse, since chromatography utilizes relatively large amounts of the material which requires analysis. Other shortcomings that are experienced when liquid chromatography is practiced include inconsistent patterns of solute movement through the system which creates uneven flows called "dead zones" and undesirable laminar mixing as opposed to bulk movement of the fluids.
Electrophoresis is another well-known procedure that enables the researcher or scientist to evaluate undetermined materials. An electric field is imposed across a length of tubing or capillary that contains a mixture of the unknown sample and a non-reactive liquid often called a buffer solution. The electric field causes the constituents of the unknown sample to migrate through the capillary due to the electrical attraction created by the field. Different components within the sample, however, are attracted at different rates due to their varying molecular drag and varying net electrical charges. Because dissimilar substances do not react to the drag and electrical attraction in the same way, they become increasingly separated into distinct zones or groups as they progress along the capillary. Each band of constituent material that makes up the original unseparated mixture of unknown material passes through the capillary by itself. At some point along this tubing, each band is examined and identified by a detector. One type of detector for electrophoretic separations measures the electrical conductivity of the bands in the capillary. An alternative detection scheme is a method called laser induced fluorescence. Although this technique is highly sensitive, it is costly and is limited to detecting compounds that fluoresce or which can be stimulated to do so. Another previous system probes the unknown material by shining light through the material and then gauging how much light is absorbed by the material. Unfortunately, the short and narrow path that the light travels across the capillary does not provide many opportunities for the undetermined sample to absorb photons. The capillaries must be kept very narrow so that all the material inside it moves easily without turbulence or eddy currents that might be caused by uneven radial heating across a larger tube. As a result of this size constraint, one major problem that plagues this approach is low detection sensitivity.
As the technology of genetic engineering continues to evolve, diagnostic and measurement techniques which are more accurate, reliable, and sensitive become increasingly more valuable. Doctors, clinicians, and laboratory technicians need more powerful tools to explore the intricacies of the genetic code, to improve the hardiness and usefulness of plant and animal life in an effort to feed the world's burgeoning population, and ultimately to devise cures for inherited disabilities and dreaded diseases. The problem of providing a highly sensitive and precise biological detection and analysis system that overcomes the limitations that impair previous devices and techniques has presented a major challenge to designers and innovators in the biochemical arts. The development of an effective, sensitive, affordable, and unerring system for sensing the components of an unspecified biological sample would constitute a major technological advance in the biochemical and biotechnology industries. The enhanced performance that could be achieved using such an innovative device would satisfy a long felt need within the business and would enable manufacturers of drugs, medicines, and biological products to save substantial expenditures of time and money.